Increasing capacity of a semiconductor memory and increasing speed and density of a CPU processor have inevitably necessitated further improvements in fineness of microprocessing through optical lithography. Generally, the limit of microprocessing with an optical lithographic apparatus is on an order of the wavelength of light used. Thus, the wavelength of light used in optical lithographic apparatuses has been shortened more and more. Currently, a near ultraviolet laser is used, and microprocessing on the 0.1 μm order is enabled. While the fineness is being improved in the optical lithography, in order to assure microprocessing of 0.1 μm or narrower, there still remain many unsolved problems, such as further shortening of laser wavelengths, development of lenses usable in such a wavelength region, and the like.
On the other hand, as a measure for enabling microprocessing of 0.1 μm order or narrower, a microprocessing apparatus using a structure of a near-field optical microscope (scanning near-field optical microscope: SNOM), has been proposed. An example is an exposure apparatus in which, by use of evanescent light leaking from a fine opening of a size not greater than 100 nm, local exposure that exceeds the light wavelength limit is performed to a resist.
However, since such a lithographic apparatus with an SNOM structure is arranged to execute the microprocessing by use of one or more processing probes, as in continuous drawing there is a problem that the throughput is not high.
As one method for solving such a problem, U.S. Pat. No. 6,171,730 proposes an exposure method in which a photomask, having a pattern arranged so that near field light leaks from a light blocking film, is closely contacted to a photoresist upon a substrate, whereby a fine pattern of the photomask is transferred to the photoresist at once.
The method and apparatus disclosed in the aforementioned U.S. patent is very useful and it makes a large contribution to the technical field to which the present invention pertains.
Also, Japanese Laid-Open Patent Application No. 11-317345 and U.S. Pat. No. 6,497,996 disclose that such near field light has a property that the intensity is attenuated as with an exponential function, with the distance from the fine opening, and, thus, the film thickness of a pattern forming layer based on the near field exposure has to be made thin.
FIG. 2 illustrates a near-field electrical field distribution around a mask opening obtained by investigation made through simulations. Specifically, FIG. 2 shows the state of an electrical field distribution produced adjacent to the opening, where light having a wavelength of 436 nm is projected to a near-field exposure mask having a pitch of 200 nm and a mask opening width of 70 nm. Values in the drawing are relative electrical field intensities at respective positions where the intensity of incident light is taken as one.
Seeing the electrical field distribution, there is an extension from the opening to the light blocking film portion. This means that there is a possibility that the opening pattern of the mask and the pattern provided by exposure do not completely correspond to each other.
The feature that the electrical field intensity attenuates as coming away from the mask opening and that there appears an electrical field distribution being extended in a direction parallel to the mask surface, such as depicted in FIG. 2, is peculiar to the near field.
Generally, making an exposure mask takes a very long time and is expensive. In the mask pattern production for near field exposure, particularly, the mask design should be done while taking into account this electrical field distribution.
On the other hand, as the pattern width to be produced becomes narrower, the mask design should be made while more exactly taking into account the extension described above.
However, if the mask opening width having an electrical field distribution that can meet various pattern linewidths and pitches is sought through complicated simulations using many varieties of parameters, it takes a long time to complete the simulation and analysis. Consequently, it causes a problem that the mask designing also requires a long time.